The present invention relates to anti-skid brake control systems for wheeled vehicles, and more particularly to an improvement of the system of a type comprising a cut-off valve and a hydraulic capacity controller disposed within a hydraulic braking cirucit connecting a master cylinder to wheel brake cylinders, wherein in an anti-skid operation, the cut-off valve interrupts fluid communication between the master cylinder and the wheel cylinders and then the capacity controller is conditioned for its pressure decreasing operation for effecting the anti-skid operation.
In the conventional anti-skid brake control system of this kind, the hydraulic capacity controller includes a plunger axially movable within a cylinder casing disposed within the braking circuit and operatively connected at both ends thereof with the cut-off valve and a servo-motor respectively. The plunger is operated by the servo-motor to increase the capacity of the casing on activation of the cut-off valve thereby to decrease the pressure in the braking circuit, In this assembling construction, it is necessary that the capacity of the cylinder casing be increased by retraction of the plunger to decrease the braking pressure applied to the wheel cylinders from the maximum value to the minimum value Particularly, the retracting stroke of the plunger is mainly consumed to reduce the braking pressure to a low value. As a result, the axial length of hydraulic capacity controller becomes large and the servo-motor requires large amount of vacuum.